Less rain, more water in ponds: a remote sensing study of the dynamics of surface waters from 1950 to present in pastoral Sahel (Gourma region, Mali)

Changes in the flooded area of ponds in the Gourma region from 1950 to present are studied by remote sensing, in the general context of the current multi-decennial Sahel drought. The seasonal and interannual variations of the areas covered by surface water are assessed using multi-date and multi-sensor satellite images (SPOT, FORMOSAT, LANDSAT-MSS, –TM, and -ETM, CORONA, and MODIS) and aerial photographs (IGN). Water body classification is adapted to each type of spectral resolution, with or without a middle-infrared band, and each spatial resolution, using linear unmixing for mixed pixels of MODIS data. The high-frequency MODIS data document the seasonal cycle of flooded areas, with an abrupt rise early in wet season and a progressive decrease in the dry season. They also provide a base to study the inter-annual variability of the flooded areas, with sharp contrasts between dry years such as 2004 (low and early maximal area) and wetter years such as 2001 and 2002 (respectively high and late maximal area).The highest flooded area reached annually greatly depends on the volume, intensity and timing of rain events. However, the overall reduction by 20% of annual rains during the last 40 years is concomitant with an apparently paradoxical large increase in the area of surface water, starting from the 1970's and accelerating in the mid 1980's. Spectacular for the two study cases of Agoufou and Ebang Mallam, for which time series covering the 1954 to present period exist, this increase is also diagnosed at the regional scale from LANDSAT data spanning 1972–2007. It reaches 108% between September 1975 and 2002 for 91 ponds identified in central Gourma. Ponds with turbid waters and no aquatic vegetation are mostly responsible for this increase, more pronounced in the centre and north of the study zone. Possible causes of the differential changes in flooded areas are discussed in relation with the specifics in topography, soil texture and vegetation cover over the watersheds that feed each of the ponds. Changes in rain pattern and in ponds sedimentation are ruled out, and the impact of changes in land use, limited in the area, is found secondary, as opposed to what has often been advocated for in southern Sahel. Instead, major responsibility is attributed to increased runoff triggered by the lasting impact of the 1970–1980's droughts on the vegetation and on the runoff system over the shallow soils prevailing over a third of the landscape

Time Budget on Major Activities of Livestock Grazing Heterogeneous Natural Range and Crop Fields in Semi-Arid Nigeria

Semi-arid rangelands of West Africa provide herbs, trees and shrubs, which together with crop residues form the main sources of feed for the livestock population. Feed supply in this region is characterised by a progressive decline in quantity and quality with advancing dry season. It was reported that walking ability as well as watering frequencies affect the productivity of grazing livestock (Dicko and Sangare, 1984). This study tests the hypothesis that advancing season increases both time spent walking as well as feeding, with a switch from grazing to browsing

Population genetic responses of wild forage species to grazing along a rainfall gradient in the Sahel: A study combining phenotypic and molecular analyses

Abstract Genetic diversity was studied in wild forage species subjected to grazing along a rainfall gradient in West Niger, within the Sahel with aim of identifying adapted genotypes, which could be used to reclaim degraded land. Two legumes (Alysicarpus ovalifolius and Zornia glochidiata) and two grasses (Brachiaria xantholeuca and Cenchrus biflorus) were selected to relate phenotypic adaptation to genetic diversity in response to grazing and rainfall. Populations of each species were sampled from both heavily grazed and ungrazed sites along a rainfall gradient, approximating 200 mm yr -1 to 800 mm yr -1 rainfall isohyets. The adaptative phenotypic expressions to aridity and grazing of the populations from each of the species were characterised by morphological measures performed on the plants sampled in the field. These analyses were then compared with the results from genetic analyses using the PCR-based techniques of amplified fragment length polymorphism (AFLP) and random amplified * Equal contribution to this work by both authors. R. Jamnadass ( ) · A. Muchug

Fertility management and landscape position: farmers' use of nutrient sources in western Niger and possible improvements

Poor millet growth and yields in Niger are commonly attributed to rainfall deficits and low soil nutrient content. Land management by local farmers is done as a function of soil types, crops, and available resources. Farmer management practices in millet fields located on four different landscape positions were studied in a village in western Niger located near the 600 mm isohyet. Average distance from homestead to field was 980 m, with fields in the valley bottom much closer (average 225 m) and fields on the plateau much further (average 2300 m). Farmers considered the valley and plateau fields slightly more fertile than the other fields, but rainfall infiltration on plateau fields is often relatively poor. Nitrogen and phosphorus contents in the soil were highest on the less intensively cropped plateaus. More than 50% of the fields did not receive any applied nutrients other than during livestock grazing of leftover stover. Manure application was done through corralling in only four of the fields studied (20%), out of which three were farmed by Fulani using their own herds for manuring. There was no significant effect of landscape unit on yield, though yields in the valley and on the upper slope were slightly higher than average. Millet grain yields, soil carbon and soil phosphorus decreased significantly with distance from the living quarters. This may be because manuring usually takes place close to home (average distance in 1997 <200 m). Manure application increased millet grain production from 126 kg ha−1 to 316 kg ha−1 in 1997. Manuring yielded more than 1000 kg ha−1 in 1996, when rainfall was much more favourable. Fallowed fields yielded an average 143 kg ha−1 of millet grain in 1997, with fallow taking place an average of 1640 m from the homestead. Another soil fertility management practice included use of millet threshing residues in fields adjacent to the village. There was no chemical fertilizer application. Any improvement to the system will require the solution of existing constraints limiting the integration of livestock and crops and/or limiting the input of external sources of nutrients in Niger. These limitations can include lack of land to allow fallowing practices and/or grazing; local non-availability of mineral fertiliser; lack of capital to buy fertiliser, due in part to low millet prices; lack of means of transport for inputs; but also lack of means for pest control and lack of labour for sowing, weeding and thinning. Initial improvements may be made by making more efficient use of the available manure, through much lighter and slightly more frequent manuring of much larger area